Project summary Sleep health is a public health priority. Socioeconomic and ethnoracial differences in sleep (?social disparities in sleep?) across childhood and adolescence may contribute to the emergence and persistence of health disparities into young adulthood, a transitional period dense with many key life events. Leveraging the Fragile Family and Child Wellbeing Study (FFCWS) data collection, the proposed research will investigate the longitudinal behavioral, sociodemographic, and contextual predictors of young adult sleep health, and the extent to which youth sleep health trajectories and other health behaviors contribute to disparities in young adult wellbeing. As a sub-study of the age 22 wave of the FFCWS, this renewal proposal will collect sleep and health behavior data in Aim 1. First, we will add sleep-related questions to the age 22 young adult general survey in the full FFCWS cohort (n~3600). Then, on a subsample of approximately (n~900) adolescents who participated in the age 15 actigraphy data collection, we will collect 14 days of actigraphy data for sleep and physical activity, with a concurrent smartphone-based, twice-daily diary app collecting screen use and self-reported activity data (e.g., substance use, diet). This study enables the first actigraphy-based analyses of sleep trajectories from adolescence into young adulthood. In Aim 2, we seek to identify the magnitude of sleep health disparities in young adulthood, and the extent to which contextual and behavioral factors account for social disparities in sleep. We hypothesize that ethnoracial minorities and those with early life lower SES will continue to exhibit poorer sleep health in young adulthood, and that these differences are partially accounted for by family and contextual factors, sleep and health behaviors, and the autonomy and constraints of young adulthood. In Aim 3, we will assess how sleep health trajectories across childhood and adolescence are associated with wellbeing in young adulthood, including physical health, social-emotional health, and socioeconomic wellbeing. In Aim 4, we will model within-person temporal dynamics between health and health risk behaviors (i.e., physical activity, pre-bed screen time, substance use, diet) and sleep health using two weeks of actigraphy and daily diary data. Here we hypothesize that, within a person, engaging in health risk behaviors (e.g., pre-bed screen time, sedentary activity, substance use) will adversely affect that night?s sleep, and that positive health behaviors (e.g., physical activity) will benefit that night?s sleep. We further hypothesize that sleep has within-person effects on next-day activities (e.g., more sleep duration is associated with more next-day physical activity). The proposed rigorous actigraphy-based investigation of sleep trajectories from childhood through age 22 advances our understanding of social disparities in sleep health and wellbeing in young adulthood. Mechanistic insights regarding the role of modifiable behaviors (e.g., bedtime routines, screen use behaviors, physical activity, substance use, diet) and contextual factors can influence the development, implementation, and evaluation of policies and interventions to reduce sleep and health disparities and improve wellbeing of young adults.